Volume-control means for radioreceivers and the like



March'3l, 1931. 5, BRADBURY' 1,799,000

VOLUME CONTROL MEANS FOR BADIORECEIVBRS AND THE LIKE Filed Nov. 19, 1928 Inventor B UTK e B radburg, by I bf wl Hns Attorneg.

Patented Mar. 31, 1931 UNITED STATES PATENT OFFICE.

BURKE BRADBUBY, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK VOLUME-CONTROL MEANS FOR RADIORECEIVERS AND THE LIKE Application filed November 19, 1928. Serial No. 320,369.

vide an improved means for controlling the operation of such apparatus when subjected to extremely strong signals, such as signals from a local broadcasting station for ex ample.

It 1s customary 1n certain types of receivers, such as tuned radio frequency recelvers for example, to provide a volume control means in the input circuit of the first tube thereof and to provide an untuned inductor in the antenna circuit with which this input circuit is directly connected. This type of volume control usually comprises a variable resistance connected in shunt with the input or antenna circuit or the antenna inductor. In the reception of strong local signals this volume control arrangement alone has, in certain instances, been found to be inadequate to control the receiver, for the reason that the variable resistance has the effect of a variable load u oon the antenna inductor, and

for the higher requencies tunes the inductor to the signal frequency, so that the maximum resistance does not always correspond to maximum volume.

In accordance with the invention, a tuned link circuit is interposed in the receiver at a suitable point, for controlling the transfer of energy therethrough, and. such circuit is provided with means whereby the signal strength may be varied withoutaffecting the tuning of the set or of the link circuit.

My invention will be better understood from the following description when considered in connect1on with the accompanymg drawing, and its scope will be pointed out in the appended claims.

In the drawing the figure is a wiring diagram of a tuned radio frequency receiver provided with a volume control means embody ing the invent1on.

Referring to the drawing, 5, 6 and 7 are radio receiving tubes representing any sultable electrlc discharge devices, connected 1n cascade betweenan input circuit 8 andan output circuit 9, by suitable tuned radio frequency transformers 10, 11 and 12. In this present case the tubes 5 and 6 are represented as being of the screen grid type. My invention is particularly applicable to use with radio frequency amplifying tubes of this type although it is not limited to use with such tubes. v

In the. present example tube 7 is the detector tube and is provided ,with an output transformer 13 forconveying its output to associated apparatus (notshown) while tubes 5 and 6 are radio frequency amplifiers of the screen grid type. The tubes receive their operating current and potentials from supply leads indicated at 14, 15 and 16.

The input circut is connected with the control grid of radio frequency tube 5 and receives signal voltage fromany suitable source such as an antennallconnected to ground through an antenna inductor 1 8. Across the input circuit and in this case across the antenna inductor, is connected a variable resistor 19. This resistor may be of any suitable type and in the present example is of the sliding arm type, having an arm 20 pivoted at 21 and provided with an extension 22, the arrangement being such that movement of the extension to the right causes the arm to move along the resistor to increase the resistance across the input circuit, thus increasing the signal voltage applied to the receiver.

The above-described receiver may be regarded as representing any electrical apparas tus having an input circuit and associated circuits through which energy is transmitted from said input circuit. 1

In accordance with the inventionan improved coupling or link circuit 23 is provided between the radio frequency transformers 10 and 11. This circuit includes the secondary 24 of radio frequency transformer 10, a variable tuning capacitor. 25 which is grounded at 26, the primary 27 of radio frequency transformer 11, and a resistor 28 which'is grounded at 29 at one end, together with primary 27, and which is at its opposite end connected withthe high potential end of the secondary 24. v I 1 The opposite end of the primary is connected with a movable arm 30 of the resistor 28. This arm is pivoted at 31 and is provided with an extension 32 which is connected by a link 33 with the arm 20 of resistor 19.

The above-described circuit arrangement may be considered to be divided into two parts, a tuned section which includes the inductor or secondary 24- and the tuning capacitor 25, which section is in efiect connected across or in series with the resistor 28, and a coupling section which is the coil orprimary 27 the latter being variably connected or coupled electrically with the tuned section by movement of the contact arm 30. Movement of the contact arm 30 to the right or the eX tension of the arm 32 to the left thus causes a reduction of the resistance across or in shunt connection with the coupling section and a reduction of the coupling or of the voltage applied across said section.

It will thus be seen that the signal energy or voltage applied to the tuned circuit will be applied across the terminals of the resistor 28 which forms a connecting means between the tuned section and the coupling section, and that by varying the connection with the resistor any portion of this energy or voltage may be applied to the coupling section. In this manner the tuned link circuit serves to control the volume of the signal energy being transmitted through the apparatus, and it controls the volume without afiecting the selectivity, for the reason that as the volume is reduced by decreasing the resistance across or in shunt to the coupling section or primary 27 tending to produce increased selectivity, the remainder of the resistor is inserted in the tuned circuit, tending to produce a broadening of the tuning. The two opposite effects counteract each other and the result is a control of the volume only through whatis in efiect, a control of the electrical coupling between the sections. 7 7

Through the link connection33, the resistor 19 across the input circuit is simultaneously varied in a direction to cooperate with the effect of variation of the resistor 28, so that a very effective control of the volume is provided; that is, as the resistance across the input circuit 8 is decreased to decrease the volume, the resistance across the coupling section or primary 27 is also decreased, and in a like manner when the resistance across the input circuit8 is increased, the resistance across the cou lin section or rimar 27 is increased thereby providing a control of volume simul taneously b-yboth circuits. I

This-type of volume control has been found to be veryeifective in controllingthe volume in a receiver in the presence of strong radio frequeney signals. For example, with a total resistance of 2000 ohms at 19, a total resistance of 270 ohms at 28, and with a coupling section or coil'27 of two turns associated with the low potential end of the secondary of transformer 11, this control has been found to be effective in handling an input field strength of 0.25

volts per meter, to produce normal output at broadcasting station and represents radio frequency at one volt applied across the receiver terminals or .25 volt per meter of the effective height of the average antenna which is, for purposes of comparison, considered to be four meters. The abovefigures are given only by way of example and not many way as a limitation, the scope of the invention being defined inthe appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A volume control means for a tunedradio frequency amplifier comprising a coupling circuit including a tuned section and a coupling section, a variable resistor connected between said sections and arranged to vary si multaneously the voltage applied to the coupling section and the resistance of the tuned section whereby the selectivity of the coupling circuit is maintained substantially constan't.

2. A'volume control means for a radio frequency amplifier comprising an inputcircuit, means'for varying the resistance of said circuit, an interstage coupling circuit including tuned and coupling sections, and variable resistor means connected with each of said sections and simultaneously operable with said first named means for varying the resistance of one of said sections and the volt age applied to the other of said sections.

3. The combination with an electrical apparatus having an input circuit and associated circuits through which energy is transmitted from said input circuit, of means for controlling the flow of energy through said apparatus, comprising a variable resistor connected with the input circuit to control the energy applied therethrough, an intermediate circuit including tuned and coupling sections, and'means including a variable resistor for simultaneously varying the effective resistance. of said tuned section and thevoltage applied to said coupling section.

4. The combination with a tuned radio frequency amplifier includingelectric discharge devices, means providing an output circuit for one of said devices, and means providing an input circuit for another of said devices, of

a tunedcircuit electrically coupled with said output circuit, a resistor connected in series with said tuned circuit, a contactmovable along said resistor, a coupling coil of relatively few turns coupled with said input circuit and provided with terminals connected with one terminal of the resistor and with said movable contact respectively, whereby said tuned circuitand coupling coil are electrically connected through said resistor andcontrolled for the transmission of energy through said amplifier by movement of said contact along said resistor.

5. The combination in a tuned radio frequency amplifier, of a pair of electric discharge devices, means providing an output circuit for one of said devices, means providing an input circuit for the other of said devices, a tuned circuit electrically coupled with said output circuit, a resistor connected in series with said tuned circuit, a contact movable along said resistor, and means pro viding an electrical coupling with said input circuit connected to said resistor through one terminal of said resistor and said contact.

6. The combination with an electrical apparatus having two circuits arranged for the transmission of alternating current energy between them at a desired frequency, of a coupling circuit interposed between and adapted to electrically couple and control the flow of energy between said first-named circuits, said coupling circuit including a tuned section responsive to said desired frequency and associated with one of said first-named circuits, a resistor connected in series therewith, a coupling section associated with the other of said first-named circuits and connected in shunt with said resistor, and means for varying simultaneously and inversely one with respect to the other the resistance in said tuned section and the resistance in shunt with said cou pling section provided by said resistor, whereby the transmission of energy through said coupling circuit may be varied without substantially changing the tuning response of said coupling circuit to said desired frequency.

In witness whereof, I have hereunto set my hand this 17th day of November, 1928.

' BURKE BRADBURY. 

